The invention relates to a voltage quality assessment method for the low-voltage electrical network. A low-voltage electrical network quality assessment device is arranged, and comprises an onsite computer, the onsite computer is provided with a voltage quality assessment module, and connected with a remote monitoring computer via the wireless communication network, and the onsite computer is further provided with a dehumidifying cabinet. The method can be used to overcome the defects that the onsite computer cannot transmit data to the remote effectively, moisture in the external environment penetrates into the dehumidifying cabinet, operation state of the dehumidifying cabinet as well as the dehumidifying cabinet itself cannot be observed in real time, and parts of enclosed structures are complex.